Polyarylene sulfides are high-performance polymers that may withstand high thermal, chemical, and mechanical stresses and are beneficially utilized in a wide variety of applications. Polyarylene sulfides are generally formed via polymerization of a dihaloaromatic monomer with an alkali metal sulfide or an alkali metal hydrosulfide in an organic amide solvent. Precipitation of the polyarylene sulfide from solution will occur when the polymer reaches a particular degree of polymerization, which can vary depending upon solution conditions including temperature, pressure, solvent concentration, polymer concentration, etc.
The precipitation conditions can affect the physical, chemical, optical, and other properties of the product polymer, and variation in product properties can in turn affect critical measures of market success such as customer satisfaction and production costs. By way of example, if the precipitated polymer has a poor particle integrity (due to, e.g., low density and/or excessively high porosity), the particles will be more likely to develop fines, which can lead to low yield and increased production costs as well as explosion hazards. On the other hand, if the polymer flakes have a porosity that is too low, washing of the polymer can be less effective, and the impurity content of the product can be unacceptably high. Similarly, consistent bulk density and narrow particle size distribution of the precipitated polymer particles can improve flow of the polymer flakes during, e.g., packaging, hopper loading, etc. Unfortunately, even minor variations in the precipitation conditions can lead to large differences in the properties of the precipitated flake.
Methods have been developed to better control precipitation of polyarylene sulfides, and thus improve the desired qualities of the polymers and compositions incorporating the polymers. For instance, the use of temperature controlled jacketing around a reactor to provide a controlled, slow cooling process has proven useful in controlling characteristics of the precipitating polymer.
While such cooling processes have been developed and improved upon to better control the characteristics of precipitated polyarylene sulfides, room for further improvement exists. What are needed in the art are precipitation methods for use during polyarylene sulfide formation that can provide reliable and desirable product characteristics.